The needs for higher processing speed and greater recording capacity are growing among HDDs and other apparatus for recording signals on magnetic recording media. A considerable number of activities are observed for satisfying the needs. For the high density recording, HDDs employ a thin film head; in which an inductive head is used for recording signals, and a magnetoresistive head (MR head), or a giant MR head (GMR head), is used for reproducing signals.
A conventional thin film head is described below referring to drawings.
FIG. 16 is a perspective view showing the outline at the sliding surface of a conventional thin film head facing a recording medium. FIG. 17 shows an outline front view of the thin film head.
A lower gap layer 162 of Al2O3, AlN, SiO2 or other nonmagnetic insulating material is formed on a lower magnetic shield layer 161 made of a soft magnetic material such as Permalloy, a Co amorphous magnetic layer, an Fe alloy magnetic layer. On top of the upper surface, a magnetoresistive element 163 (an MR element or a GMR element, hereinafter both are collectively referred to as GMR element) is deposited, and a longitudinal biasing layer 164 is formed by a CoPt alloy or other such material at both the right and the left ends of the GMR element 163. A lead layer 165 of conductive material such as Cu, Cr, Ta, etc. is provided on the upper surface of the longitudinal biasing layer 164 so that the lead layer 165 makes contact with a ridge line formed by the upper surface of the GMR element 163 and the end faces. The lead layer 165 may be disposed instead on the upper surface of the longitudinal biasing layer 164 so that it covers part of the upper surface of the GMR element 163. Next, an upper gap layer 166 is formed over the lead layer 165 and the exposed region of the GMR element 163, using the same nonmagnetic insulating material as the lower gap layer 162. Further on top of the upper gap layer 166, an upper magnetic shield layer 167 is provided using the same soft magnetic material as the lower magnetic shield layer 161. This completes the reproducing part 168 of a magnetoresistive head.
On the upper surface of the upper magnetic shield layer 167, a recording gap layer 171 is formed using the same nonmagnetic insulating material as the lower gap layer 162. An upper magnetic core 172, which faces to the upper magnetic shield layer 167 via the recording gap layer 171 and makes contact with the upper magnetic shield layer 167 at the rear scene of FIG. 16, is provided in the form of a layer using a soft magnetic material. Between the upper magnetic shield layer 167 and the upper magnetic core 172 facing to each other with the interposing recording gap layer 171, a coil 173 is provided electrically isolated from both the upper magnetic shield layer 167 and the upper magnetic core 172. This completes the recording part 170 of a magnetoresistive thin film head. The upper magnetic shield layer 167 works as the shield for the reproducing part 168 and as the lower magnetic core of the recording part 170.
Recording current supplied to the coil 173 generates recording magnetic fields in the recording gap layer 171 disposed between the upper magnetic core 172 and the upper magnetic shield layer 167 of the recording head 170, for recording the signals on a magnetic recording medium. The reproducing head 168 detects signal magnetic fields from a magnetic recording medium storing the signals, and signals reproduced by the GMR element 163 in accordance with the resistance shift are taken out through the terminal of lead layer 165.
FIG. 17 shows outline front view of the reproducing part in the vicinity of magnetoresistive element of the above-described thin film head. A lower gap layer 162 is provided on the upper surface of the lower magnetic shield layer 161. On top of it, an antiferromagnetic layer 174 formed of a magnetic material such as IrMn, an FeMn alloy, a PtMn alloy, αFe2O3, or NiO; a pinning layer 175 formed of a magnetic material such as a NiFe alloy, Co, a CoFe alloy; a nonmagnetic conductive layer 176 formed of a nonmagnetic conductive material such as Cu; a free magnetic layer 177 formed of the same material as the pinning layer; and an upper cap layer 166 formed of a nonmagnetic material such as Ta; are deposited sequentially. The laminated body of stacked layers is defined at both the right and the left ends by ion-milling or the like method so that each of the cut ends has a slant surface. Thus a GMR element 163 is provided.
A pair of longitudinal biasing layers 164 are formed at both ends of the GMR element 163 in physical contact with the slant end surfaces, and a pair of the right and the left lead layers 165 are provided on the longitudinal biasing layers. On top of them, an upper gap layer 166 is formed, followed by an upper magnetic shield layer 167. Thus the reproducing part 168 of a magnetoresistive thin film head is completed. Gap length 179 of the reproducing part 168 represents a total sum in the thickness of the lower gap layer 162, the GMR element 163 and the upper gap layer 166. The gap length 179 is becoming smaller, so that it is capable of reproducing the short-wavelength signals of high density recording.
With the reproducing part of the above-configured thin film head, in order to be able to reproduce the short-wavelength signals stored in a magnetic recording medium, gap length of the reproducing part needs to be sufficiently short. As described earlier, the gap length is a distance between the upper surface of the lower magnetic shield layer and the lower surface of the upper magnetic shield layer. It means that the distance is represented by a total thickness of the lower gap layer, the GMR element and the upper gap layer. The short distance means that the pair of longitudinal biasing layers disposed at both the right and the left ends of the GMR element are existing very close to the lower magnetic shield layer or the upper magnetic shield layer. Under which circumstance, magnetic fields of the longitudinal biasing layers easily escape to the lower magnetic shield layer or the upper magnetic shield layer. As a result, magnetic coupling between the longitudinal biasing layer and the free magnetic layer of GMR element becomes weak and the direction of magnetization of the free magnetic layer is not orientated in a stable manner, and noise generation increases. Thus it is difficult for a thin film head of the conventional structure to yield stable reproducing signals. The reduced width of recording track for the high-density recording brings about a minimized spacing between the pair of the right and the left longitudinal biasing layers. Under such a situation, if magnetic field of the longitudinal biasing layer is made stronger, the free magnetic layer of GMR element receives a too strong magnetic field from the longitudinal biasing layer. This leads to a problem that it makes it difficult for a free magnetic layer to change the magnetization direction in response to signal magnetic field; deteriorating sensitivity of the reproduction. Another still greater problem is that the magnetization direction of pinning layer is prone to assume the direction of track width by the influence of longitudinal biasing magnetic field.